Electro Polishing SS welds

[Will_D]

So after you have tig'd some stainless you are left with discoloured welds and adjoing metal.

The old way was to use pickling paste (a NASTY blend of Nitric and Hydroflouric acids that you really don't want to use. Local welding suppliers now don't stock this due to 'Elf'n'safety - maybe for once they are right)

My local supplier gave me a bottle of pink(!) 50% phosphoric acid (this is called the electrolyte) and a posh brochure for an "Inverter powered cleaning system" from Italy

In a nutshell its an inverter welder set to MMA (no HF sparks please) with a "brush" as the Cathode (-ve) and the workpiece is the anode (+ve) - so earth of the tig goes to work and "brush" goes into the MMA stinger.

So, proof of concept:

Make up a brush out of some s/s bits and and the green pan scourers.

Dip in acid and brush the weld.
Set to 10 amps: not a lot happening
Set to 50 amps: Lots of smoke, pan scourers melting but weld is clean.

Ok, concept works.

Now the pro tools use carbon fibre brushes (at £100 a set of 4 in UK), so some carbon  fibre tape has been obtained and brushes will be made.

Note that for Food grade cleaning non acidic, neutral, FG electolytes are used.

Any one ever tried this at home?

[PK]

We looked at it as a production process. I made some brushes much as you describe out of some CF strands pulled from some cloth and crimped into an electrical lug. (tip, you can buy CF vinyl record cleaning brushes for not much money and get quite  few smaller electro-polishing brushes out of them).
In the end it was too fiddly for a day job and we went back to a manual polish.

PK

[sparky961]

Never tried it at home but we have one where I work.  I've used it several time.... stinks like you wouldn't believe but makes nice shiny welds.  Sure beats polishing them by hand.  I've always used it with the bay door wide open or wearing a particulate mask, but I'd really like to know what the "smoke" is made of and its health effects.

[awemawson]

Is it not basically the same process as electrolytic rust removal?

After all presumably the discolouration is oxides of the metals comprising the stainless steel?

[drmico60]

Is it not basically the same process as electrolytic rust removal?

After all presumably the discolouration is oxides of the metals comprising the stainless steel?

No it is not the same as electrolytic rust removal. In electrolytic rust removal the work piece is the cathode, ie connected to the negative electrical supply whereas in electropolishing the work is the anode ie. connected to the positive supply.

In derusting the rust is reduced to black iron oxide at the cathode which is non adherent whereas in electropolishing metal and oxides are dissolved at the anode.

Mike